Ceramic materials have been utilized as friction materials for clutches for many years. In general, ceramic or cerametallic materials or sintered powdered metals are utilized in the form of discs or buttons that are uniformly distributed on a clutch base plate or other supporting element. As the material is brittle and easily fracturable, the discs or buttons are located in and supported by a metallic cup having a base adapted to be secured to the supporting element with a side wall that is initially generally cylindrical, but can be inwardly deformed to interlock with the outer edge of the disc or button to retain it in the cup. Also, the cup is secured to the supporting member to prevent rotation, or the cup has one or more projections or rivets which interact with the supporting element to prevent rotation of the friction button during use in the clutch.
The use of ceramic or cerametallic friction materials is normally designated primarily for heavy service conditions causing high operating temperatures. Under some types of heavy service, these materials are unsatisfactory due to excessive wear of the material or a tendency to score the cast iron surfaces of the flywheel and pressure plate engaged thereby. Also, smooth operation of the device in which the clutch is installed is difficult as the operator does not have the ability to control the engagement of the clutch to the requisite degree. As the material is relatively hard and offers no resiliency, the clutch is therefore either engaged or disengaged without the gradual frictional engagement found in other conventional clutch friction materials. Thus, it is substantially impossible to control the degree of smoothness of clutch engagement required for desired maneuverability.
As considerable heat is generated in service, there is a tendency for the flywheel and pressure plate surfaces to dish concavely towards each other, which will alter the loading on the friction buttons and cause uneven wear. To overcome these disadvantages, the friction buttons have been mounted on the supporting element in a manner to provide a limited degree of resilience when the buttons are engaged by the flywheel and pressure plate. However, the resilient mounting does not overcome the problem of the clutch grabbing upon engagement thereof resulting in an abrupt torque curve. The present invention overcomes the above noted problems to provide a gradual torque curve for a ceramic friction material clutch and reduce the poor or harsh feel for the operator.